Tuberculosis

Pulmonary tuberculosis is an infectious disease caused by slow- growing bacteria that resembles a fungus, Myobacterium tuberculosis, which is usually spread from person to person by droplet nuclei through the air. The lung is the usual infection site but the disease can occur elsewhere in the body. Typically, the bacteria from lesion (tubercle) in the alveoli. The lesion may heal, leaving scar tissue; may continue as an active granuloma, heal, then reactivate or may progress to necrosis, liquefaction, sloughing, and cavitation of lung tissue. The initial lesion may disseminate bacteria directly to adjacent tissue, through the blood stream, the lymphatic system, or the bronchi. Most people who become infected do not develop clinical illness because the body’s immune system brings the infection under control. However, the incidence of tuberculosis (especially drug resistant varieties) is rising. Alcoholics, the homeless and patients infected with the human immunodeficiency virus (HIV) are especially at risk. Complications of tuberculosis include pneumonia, pleural effusion, and extrapulmonary disease. TB results from infection by any of the TB complex mycobacteria, including Mycobacterium tuberculosis, M bovis, M africanum, M microti, and M canetti.5 TB can be divided into primary, progressive-primary, and postprimary forms on the basis of the natural history of the disease. Postprimary TB results from either reactivation of a latent primary infection or, less commonly, from the repeat infection of a previously sensitized host. The term “postprimary” is preferred to “reactivation” when referring to the clinical diagnosis because firmly distinguishing recurrence from an antecedent infection is impossible in most cases. Approximately 10% of all infected patients are likely to develop reactivation, and the risk is highest within the first 2 years or during periods of immunosuppression. The major determinants of the type and extent of TB disease are the patient’s age and immune status, the virulence of the organism, and the mycobacterial load. Postprimary TB is typically a disease of adolescence and adulthood that results from reactivation of an initially contained infection by a TB complex mycobacterium. Pulmonary reactivation usually occurs in the apical and posterior segments of the upper lobes or in the superior segments of the lower lobes.This distribution may be related to the higher oxygen tension or the reduced perfusion and lymphatic clearance in these lung segments. DIAGNOSTIC EVALUATION Sputum smear – detection of the acid fast bacilli in stained smears is the first bacteriologic clue of TB. Obtain first morning sputum on 3 consecutive days. Sputum culture – a positive culture for M. tuberculosis confirms a diagnosis of TB. Chest X-ray – to determine presence and extent of disease. Tuberculin skin test (purified protein derivative or Mantoux test) – inoculation of tubercle bacillus extract (tuberculin) into the intradermal layer of the inner aspect of the forearm. Nonspecific screening test – such as multiple puncture tests (tine test), should not be used to determine if a person is infected. MEDICATION ¨ A combination of drugs to which the organisms are susceptible is given to destroy viable bacilli as rapidly as possible and to protect against the emergence of drug resistant organism. ¨ Current recommended regimen of uncomplicated, previously untreated pulmonary tuberculosis is an initial phase of 2 months of bacterial drugs, including isoniazid (INH), rifampin ( Rifadin), pyrazinamide (PZA), and ethambutol (EMB). This regimen should be followed until the results of drug susceptibility studies are available, unless there is little possibilityn of drug resistance. a. If drug susceptibility results are known and organism is fully susceptible, ethambutol does not need to be included. b. For children whose visual acuity cannot be monitored, ethambutol is not normally recommended except with increased likelihood of isoniazid resistance or if the child has upper lobe infiltration and or cavity formation of TB. c. Due to increasing frequency of global streptomycin reistance, streptomycin is not considered interchangeable with ethambutol unless organism is known to be susceptible to streptomycin